Automatic damper control



Nov. 11, 1941. J. ROLAND 2,262,252

AUTOMATIC DAMPER CONTROL Filed Jan. 28, 1959 mvENToR. .fof/N Foz. H/v.

Patented Nov. 1l, 1941 AUTOMATIC DAMPEB CONTBUL John Boland,Indianapolis, Ind., assigner to Schnitzer-Cumming Company,

Ind., a corporation lndlanalwll,

Application January 28, 1939, Serial No. 253,304

3Claims.

This invention relates to an automatic damper control especiallysuitable for use with furnace stokers and the like, representing animprovement over the control described in Letters Patent A forced draftis necessary in connection with an underfeed stoker to insure propercombustion of the coal or other fuel fed into the ilre pot.

` The centrifugal blower customarily employed to furnish the forceddraft and which operates during the fuel feeding periods must be capableof supplying a suillcient quantity of air regardless of the condition ofthe fuel bed. The resistance to the passage of air oiered by the fuelbed is naturally dependent upon its compactness and depth-the morecompact and impermeable it is the more resistance it will offer. It ischaracteristic of a centrifugal blower that when the resistance againstwhich it is operating is increased the volume of air it delivers willdecrease and conversely when the resistance decreases the volumeincreases. This being so, a blower able to furnish suillcient air whenthe fuel bed is of maximum compactness, unless controlled, will supplytoo much air when the fuel bed is shallow and open, resulting in a toorapid and uneconomical consumption of fuel with the resulting dimcultiesof operation on account of clinkers forming in the burner and burningout the tuyres.

It is one object of this invention, therefore, to provide an automaticdamper control which will operate to furnish an additional resistance tothe passage of air from the blower when necessary for a constant airdelivery. Thus, when the fuel bed is of maximum compactness and depththe blower conduit will be completely open allowing free passage of theair, but when the fuel bed is otherwise the damper control willcompensate for the reduced resistance by fully or partially closing theconduit, depending upon the exact condition of the fuel bed, therebycausing the blower to work against a constant static pressure whichinsures a constant air delivery. It follows from the above that the airdelivery of a centrifugal blower operating against a constant staticpressure is constant at the same number of revolutions. Since, underordinary conditions, the

rate of fuel feed under a given setting of the.

Stoker feed is constant the quantity of air supplied should also beconstant. With this control there is no likelihood of the fuel beinguneconomically consumed under any fuel bed condition, and operatingdiiculties are eliminated and less care required for the operation ofthe stoker such as manual adjustment for outside temperatures.

'Ihe combined resistance of the fuel bed and the resistance of thedamper will make the blower work under constant pressure, thereby givinga constant volume ofair.

This and other objects are accomplished by means of the constructiondescribed in the following specification and illustrated in theaccompanying drawing:

With reference to the drawing, Fig. 1 is a diagrammatic illustration ofa furnace and Stoker showing a iirepot and blower conduit with anautomatic damper control embodying the invention appliedthereto. Fig. 2is a sectional view through a portion of the blower conduit and dampercontrol showing the damper blades in substantially open position. Fig. 3is the same as Fig. v2 except that the damper blades are in closedposition. Fig. 4. is a section on the line 4-4 of Fig. 3. Fig. 5 is aplan View of the top of the cap surmounting the damper control housing.

In the drawing, Fig. 1 shows a furnace Il having a repot Il with a bedof fuel l2 therein. Fuel is fed into the bottom of the repot from thehopperi3 by the screw ll driven by the mo-v tor l5 which also drives thecentrifugal blower i6 enclosed by the housing l1. j

Positioned on top of the blower conduit i8 and in open communicationtherewith ls the uppermost part of the damper control unit including ahousing I9 secured to the conduit by a saddle portion 20, said saddleportion being co-extensive with the cylinder portion.

In the cap 2l of the housing there is a curved aperture or vent 22which, by turning the cap on the swivel 23, can be made to coincide witha similar opening in the top of the housing. The screw 24 serves only tomake the adjustment secure and may be omitted. Thus, means are providedto restrict the flow of air from the housing l! to the atmosphere.

Reciprocal within the housing I9 there is a loosely fitting bladeregulating disc or piston 25 whichoperates to swing the damper blades 2Gand 2l. Said blades are separately and pivotally mounted on the frame28, so as to swing to closed or open position depending upon the staticpressure within the blower conduit; The control rod 29 connecting thepiston and damper blade 2B fits the bracket 30 loosely, and-the'link rod2|' is similarly connected to brackets l2 and 33.

As is apparent from the drawing. the damper blades 20 and 21 work inunison and are in open or horizontal position when the piston isuppermost in the housing (Fig.l 2) and are in vertical or closedposition (Fig. 3) when the piston rests on the seat 34.

The slot lorY vent 35 in the housing provides an additional air releasewhich makes for easier ascent of the piston when the piston is at itslowermost point and the position of the control rod is not favorableforleverage. This arrangement .further provides an immediate and .more vsensitive response of the piston to initial pressure in the air conduit.Itcan be readily seen that as the piston moves upward in the housing theexposed area of slot below the piston increases and thus the pressureurging the upward movement ofthe piston decreases. l

The normal position of the damper blades when the blower is not inoperation is vertical,

.and the blower conduit is closed to the passage of air. Upon operationof the blower sucient static pressure to raise, the piston soonaccumulates.` The upward movement of the piston swings the blades toopen position allowing the air to pass freely to the fuel bed. Shouldthe fuel bed be deep and dense the resistance offered by it will besuchas to maintain a static pressure With a' plurality of simultaneouslyactuated damper blades, the effect of the velocity of the air againstthe damper is reduced to such a point that it will respond more readilyand be more sensitive to the variations in pressure, resulting in aconstant volume of air. A more complete closure of the blower conduit.is also possible when the damper blades are in closed position. Further,by reason of the areas of the individual blades being smaller and closerto the pivot point,

' the rush of air through the conduit offers less resistance to theiroperation.

Under conditions of little heat requirement, when it isv desirable torestrict the'draft even when the fuel bed is of near maximum compactnessthe aperture 22 should be practically closed to cause pressure to buildup on the upperside of the piston,y thus reducing the volume of airdelivered. This permits regulating of the total air volume necessary forthe type and amount of fuel fed to the fuel bed and makes a. greaterstatic pressure' necessary to raise the piston, whereby the conduit willbe less frequently open.

The invention claimed is:

1. In a forced draft regulator, an air conduit, a movable damper in saidconduit, a housing on said conduit in communication with the latter, apiston in said housing movable by air pressure therein, a control rodoperatively connecting said piston with said damper, said damper beingin closed position when the piston is retracted and openingprogressively as the piston advances, and said housing having anelongated vent in one side disposed parallel to the path of travel ofsaid piston and so positioned that the effective area thereof beyond thepistonis progressively decreased as the piston advances; theconstruction and arrangement rendering the piston more sensitive topressure within the conduit yin its retracted position and progressivelyless sensitive to such pressure as the piston advances.

2.In a, forced draft regulator, an air conduit, interconnected damperblades movably mounted for simultaneous operation in said conduit toclose the latter to the passage of air when in one position and to opensaid conduit when in another position, a housing on said conduit incommunication with the latter, a piston movably mounted in said housing,a control rod'operatively connecting said piston with said blades, andsaid housing having an elongated vent in one side disposed 4parallel tothe path of travel of said piston and so positioned that the effectivearea thereof beyond the piston is progressively decreased as the pistonmoves outwardly; the construction and arrangement rendering said pistonmore sensitive to pressure within the conduit in its initial retractedposition and progressively less sensitive to such pressure as the pistonadvances.

y 3. In a forced draft regulator, an air conduit, a movable damper insaid conduit, a housing on said conduit in communication with thelatter, a piston in said housing movable by air pressure therein, acontrol rod operatively connecting said piston with said damper, saiddamper being in closed position when the piston is retracted and openingprogressively as the piston advances,

said housing having a restrictable air relief opening in the end of thehousing remote from the conduit to regulate resistance to the outwardmovement of the piston, and said housing having an elongated vent in oneside disposed parallel tothe path of .travel of-said piston and sopositioned that the effective area thereof beyond the piston isprogressively decreased as the piston advances, the construction andarrangement rendering the piston more sensitive to pressure within theconduit in its retracted position and progressively less sensitive tosuch pressure as the piston advances.

JOHN ROLAND.

